THE FLOWER 211 
contain pistils, but no stamens ; they are, therefore, not petals, 
but the corollas of imperfect flowers. Look at the upper edge 
of a ray of sneezeweed, coreopsis, arnica, chicory, etc., for 
small teeth or notches ; these represent the lobes of a sympet- 
alous corolla. Split one of the tubular corollas of the disk 
down one side and open it out flat; does it throw any light 
on the morphology of the ray? In many composite plants, 
as the sunflower, coneflower, coreopsis, the rays are all neutral ; 
that is, they have neither pistil nor stamens. Are they of any 
use in such cases? If you are in doubt, remove all the rays 
from a head; would the disk be noticeable enough to attract 
attention without them? What is the principal office of 
the rays? 
232. The involucre. — Look at the cluster of green, leafy 
scales on the under side of the head. It is not a calyx, but 
a collection of bracts, called an involucre. Have you ever 
noticed the bracts under the separate flowers on a raceme? 
(161.) What would be the position of the bracts if all the 
flowers of the raceme were compacted into a head like the 
daisy or sunflower? Is the involucre of any use? Cut it 
away gently so as not to disturb the other organs and see 
what happens to the rays. 
233. The disk flowers. — Cut a vertical section through 
the head of a flower and notice the broad, flat receptacle (in 
some cases round or columnar) on which the tiny florets 
are seated. Observe whether it is naked, or whether it 
bears chaffy scales inclosing the florets. Make an enlarged 
drawing of this section, showing the insertion of the dif- 
ferent parts and labeling them all correctly. What differ- 
ences do you observe between the disk and the ray flowers? 
234. The pappus. — Open one of the disk flowers with a 
dissecting needle and observe the small striate (in some 
specimens, hairy) body to which the base of the style is at- 
tached. This is the ovary, inclosed in the lower part of the 
calyx, which has become incorporated with it. When mature, 
it will form a small, one-seeded fruit called an akene. Can 
